1. Field of the Invention
The present invention relates generally to contour measuring probes for coordinate measuring machines (CMMs); and more particularly to a contour measuring probe using a relatively small measuring force for contact-type contour measuring devices.
2. Discussion of the Related Art
Manufactured precision objects such as optical components (for example, aspherical lenses) and various industrial components need to be measured to determine whether manufacturing errors of the objects are within acceptable tolerance ranges. Such manufacturing errors are differences between design dimensions of the object and actual dimensions of the manufactured object. Measured dimensions of the manufactured object are usually regarded as the actual dimensions. A precision measuring device is used to measure the objects; and the more precise the measuring device, the better. Generally, the precision objects are measured with a coordinate measuring machine (CMM), which has a touch trigger probe that contacts the objects. A measuring force applied to the touch trigger probe of the coordinate measuring machine should be small and steady. If the measuring force is too great, a measuring contact tip of the touch trigger probe is easily damaged and causes a measuring error. If the measuring force is not steady, a relatively large measuring error occurs.
As indicated above, a contact-type coordinate measuring device is commonly used to measure dimensions of precision objects such as optical components and certain industrial components. A measuring force is provided to the touch trigger probe by the coordinate measuring device. However, if the object has a slanted surface, the contact tip of the touch trigger probe may become bent or deformed by a counterforce acting on the touch trigger probe, thereby causing a measuring error. Therefore, the touch trigger probe is not ideal for measuring precision lenses having slanted surfaces.
Nowadays, two methods are generally used to reduce a measuring force on the touch trigger probe. In a first method, the contact tip is slantingly arranged so that a component force of gravity acting on the measuring contact tip is regarded as a measuring force. The contact tip is very light, so the measuring force is very small accordingly. However, if a slanted angle of the contact tip changes during measuring, the measuring force changes, which makes the measuring force difficult to control. In a second method, the touch trigger probe is configured with a spring. An elastic force of the spring is regarded as a measuring force. However, when the contact tip moves upward and downward along the surface of the object being measured, a vibration of the upward and downward movement may cause the spring to resonate and deform. Therefore, the measuring force varies with the deformation of the spring. Thus both methods are subject to errors occurring in the measurement results.
In another kind of probe, a measuring force is provided by an air pump. However, the air pump provides pulsed pressure. Therefore, the air pump cannot provide a small, steady measuring force.
Therefore, a contour measuring probe employing a relatively small, steady measuring force is desired.